| Reaction characteristics of Cr(â…¢) oxidized by several Fe-Mn nodules in soil from China and several influence factors such as pH, ion strength, temperature, P/ Cd/ Pb ions adsorbed and organic acid were studied by means of balance-adsorption method and kinetic flow method. The main results were shown as follows: 1. The sequence of maximum amount(mmol/kg) of Cr(â…¢) oxidized by Fe-Mn nodules was: Nl-l(64.9) > N4-l(62.4) > N2-l(60.0) > N5-l(32.4), According to the content of Mn in nodules dissolved with 0.1mol/L NH2OH HCl, that sequence by Mn minerals in nodules was N4-1 > N2-1 > Nl-1 > N5-1. The result showed the capacity of Cr(â…¢) oxidized by MnO2 depended on the mineralogy of Mn minerals, and content of Mn4+ in Mn minerals. The Ithiophorite was main composition in Nl-1, birnessite and Ithiophorite in N2-1 and N4-1, todorokite and Ithiophorite in N5-1, so the capacity of Cr(â…¢) oxidized by Mn minerals in order was birnessite > Ithiophorite > todorokite. The amount of Mn2+ released in order was N2-1 > N4-1 > N5-1>N1-1.2. Kinetic data of Cr(â…¢) oxidized and Mn2+ released could be fitted with power function equation, parabola diffusion equation, Elovich equation, exponent function equation and first-order equation. Moreover power function equation was best. The result showed that the reaction processes was controlled by diffusion of Cr(â…¢) and Mn2+ , and surface of MnO2 covered-degree by Mn2+. A and K values of power function equation suggested that the speed of this reaction was high firstly and decreased gradually. The speed of interaction between Cr(â…¢) and nodules was different due to the different types of Mn minerals, and the speed in order was N2-1 > N4-1 > N5-1 for Cr(â…¢) oxidized, N2-1 > N5-1 > N4-1 for Mn2+ released.3. The amount of Cr(â…¢) oxidized and Mn2+ released decreased as pH increased at pH 2-6, and this decreasion in low pH was apparently higher than that in high pH.The reason was that H+ was involved in the redox reaction, and the activity of Cr(â…¢) and Mn02 increased in low pH. The effects of pH on amount of Mn2+ released was more conspicuousness than that of Cr(â…¢) oxidized, and that the order was N4-1 > N2-1 > N5-1 for Cr(â…¢) oxidized, N2-1 > N4-1 > N5-1 for Mn2+ released.4. The amount of Cr(â…¢) oxidized and Mn2+ released increased as ion strength decreased. It was related to the electric double layer of MnO2 compressed with ion strength increased, which resulted in the amount of Cr(â…¢) adsorption increasion on MnO2.5. The amount and speed of Cr(â…¢) oxidized increased as the temperature increased. The effect of temperature on Cr(â…¢) oxidized in high temperature was larger than that in low temperature. The result suggested the redox reaction was a process of decalescence. The diffusion process was main step according to reactive activation energy of the redox reaction.6. The amount of Cr(â…¢) oxidized affected slightly by P, Cd ions adsorbed on Mn minerals, but it decreased greatly as the amount of Pb2+ adsorbed on nodules increased. The amount of Cr(â…¢) oxidized reached steady values when the amount of Pb2+ adsorbed on nodules was above 100mmol/kg for N2-1/N4-1, and 200mmol/kg for N5-1. The effects of Pb2+ adsorbed on nodules for percentage of Cr(â…¢) oxidized by nodules in order was N4-1>N2-1>N5-1. It was attributed to the surface active sites of MnO2 occupied by Pb2+ priority. The balance time of redox reaction were delayed after Pb2+ adsorbed on Mn mineral.7. The amount of Mn2+ in nodules dissolved by organic acid in order was lemon acid > tartrate > phenol. The amount of Cr(III) oxidized by nodules was influenced by organic acid in the order tartrate > lemon acid > phenol, acetic acid didn't decrease the amount of Cr(â…¢) oxidized, that was related which the capacity of MnO2 reduced in order tartrate > lemon acid > phenol; and that of Mn2+complxed was lemon acid > tartrate > phenol.
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